Magneto-optically controlled ionization tube

ABSTRACT

An ion valve has two coaxial electrodes between which is a closed volume filled with pressurized gas through which an electric arc passes. Remote ignition of arc is achieved by means of a laser beam sent into the interelectrode gap. The arc is shut off by means of a magnetic field of short duration, pointed parallel to the axis of the electrodes.

I United States Patent Andre Dubois Orsay, France Jan. 9, 1970 Jan. 4, 1972 Compagnie Generale DElectricite Paris, France Inventor App]. No. Filed Patented Assignee MAGNETO-OPTICALLY CONTROLLED IONIZATION TUBE 1 Claim, 8 Drawing Figs.

us. Cl. 315/149, 328/253 Int. Cl nosb 37/02 Field ofSearch 313/157; 315/149, 344, 346, 348; 328/253 [56] References Cited UNITED STATES PATENTS 3,294,970 12/1966 .Ienckel 315/149 X 3,411,044 11/1968 Langhein et a1. 315/149 2,352,231 6/1944 Stratton 328/253 3,215,939 1 H1965 Boucher 328/253 Primary ExaminerRoy Lake Assistant Examiner-Lawrence J. Dahl AttorneySughrue, Rothwell, Mion, Zinn & Macpeak 1 a 1 ABSTRACT: An ion valve has two coaxial electrodes between which is a closed volume filled with pressurized gas through which an electric arc passes. Remote ignition of arc is achieved by means of a laser beam sent into the interelectrode gap. The are is shut off by means of a magnetic field of short duration, pointed parallel to the axis of the electrodes.

PATENTED JAN 41972 SHEET 1 OF 4 mm "72 7 alssslosv PATENTEDJAH 4:972 3.633.067

' SHEET 4 UF 4 MAGNETO-OPTICALLY CONTROLLED IONIZATION TUBE This invention concerns an ionization tube comprising two electrodes, the conductivity of which is varied, and between which is a gas under pressure and the applications of such a tube, more particularly to the conversion of direct currents into alternating current and vice versa, with transfer of electrical energy from one to the other form of current. It relates more particularly to the association of means arranged externally of the said tube for controlling both the striking of an electric arc and its extinction through the gas under pressure which it contains.

Gas-filled tubes, in which the control is effected by an electric field, produced, for example, in the thyratron type, by placing a grid between the two electrodes, the potential of which grid being varied for this purpose, but it is then necessary to accept the limitations, with respect to both voltage and current and high-time constant, which such devices involve.

Gas tubes are also known, in which a magnetic field is used for controlling ionization of gas, and consequently ensuring the operation of the tubes.

It is the aim of the present invention to utilize all the possibilities of remote control as regards both the starting and extinction of a discharge under arcing conditions between two electrodes, so as to ensure substantial independence between the volume containing the electrodes and the means for the corresponding control and regulation of the conductivity of the gases in the gap separating the electrodes.

For this purpose, use is made of coherent electromagnetic radiation emitted by a laser-type source, for initiating an are between electrodes raised to a suitable potential difference, when the beam is directed on or in the gap separating them.

On the other hand, the use of the high pressures obtained by enclosing the electrodes in a space sealed hermetically by insulating walls arranged at their two ends, ensures stability of i the electric are so produced. Once the arc is struck, the currents then determined by the external circuit and passing through the tubes are no longer limited except by the possible heat dissipation of the electrodes.

Finally for controlling the extinction of the arc, which is difficult to produce apart from the case where the electrodes are brought to the same potential, a variable magnetic field is produced by means of a low-inductance coil surrounding the external electrode and generating the field, whose lines of force are perpendicular to those of the electrostatic field prevailing between the said electrodes.

The present invention concerns an ionization tube comprising two electrodes raised to different potentials, forming between them a sealed enclosed space containing a gas under pressure, and provided with remote control means. The invention is characterized in that the ignition of the electric arc is controlled by a device emitting coherent electromagnetic radiation of laser type and projecting a beam into the interelectrode space, and in that the control of the extinction of the arc is effected by a magnetic field created by means of an external coil device surrounding the electrodes. The aims and advantages of this invention will appear from the following description with reference to the accompanying drawings, in which:

FIG. 1 shows in axial section an ionization tube according to the invention,

FIG. 2 shows a cross section of the same tube,

FIG. 3 shows in axial section an ionization tube with superposition of a constant magnetic field,

FIG. 4 represents a single-phase rectifier circuit having two ionization tubes,

FIG. 5 shows the voltage wave rectified by the device of FIG. 4,

FIG. 6 represents the spatial arrangement of ionization tubes in a GRETZ circuit,

FIG. 7 represents a single-phase inverter having two ionization tubes,

FIG. 8 shows the voltage and current waves obtained at the output of the inverter of FIG. 2.

In FIG. I, the ionization tube comprises a cylindrical internal electrode l and a substantially cylindrical exterhal electrode 2, coaxial with the first electrode, while the space 3 between them and confined at either end by insulating parts t is filled with gas under pressure. A coherent light-producing device 5 of laser type sends a beam 6 of electromagnet waves into the space 3, after concentration by the optical device 7 and passage through the window 8 of material transparent to the electromagnetic radiation and arranged in a gastight manner on an opening provided in the electrode 2. The production of the beam 6 at the desiredmoment ensures ionization of the gas. A low-inductance coil 9 surrounds the outer electrode 2, and produces between these electrodes a variable magnetic field parallel in direction to the axis of symmetry of the electrodes and intended to produce the extinction of the arc. For this purpose, the coil 9 is connected by its terminal to a pulse source. The electrodes 1 and 2, by means of conductors 111 and 12, to which they are respectively connected, are raised to different potentials, while the spherical parts 13 and toroid M are intended to eliminate the corona discharge efiect to which the angular points of the corresponding electrodes would give rise. Finally, edge effects are eliminated by the flared form of electrode 2 at both ends tending to collect the discharge in the middle part of the tube, due to the action of an electric field component parallel to that of the magnetic field, but directed inwardlly of the device.

In FIG. 2, the electrodes l and 2 are cut respectively at 15 and 16 to avoid circulation currents which would not fail to be produced as the result of variations of the magnetic field, during which the electrodes would behave like single, closed transformer turns. Gastightness of the interelectrode space is' ensured by plugging the openings thus provided with a filled insulating polymerizable resin, 17 and 18 respectively, of type known by the trade name of Araldite. The slits made in the electrodes are not shown in FIG. l for the sake of clarity.

The manner in which the magnetic [field produces blocking of the tube is explained on the basis of the representation of the trajectories of the electrons emitted by the electrode I, taken as cathode, after ignition by the laser beam. The trajectories of the electrons in the interelectrode space are rectilinear in the absence of a magnetic field and are represented by dashline radial arrows 19, passing from the cathode to the electrode 2 serving as anode. By the effect of the bombardment of the molecules of gas under pressure by the electrons, the molecules are ionized and are attracted by the cathode along rectilinear trajectories 20. The application of a rearwardly directed magnetic field as indicated at 23 results in curvature of the trajectories of the electrons which, with sufficient value Bc of the field, called the critical value, assume substantially the form of cycloids 21, showing that an electron, emitted by the cathode, returns to the latter when it has not encountered a gas molecule; however, a value Bo much more considerable than the critical value Bc is required for stopping the ionizing bombardment; this is produced for the cycloids 22 then described, on which the electrons remain close to the cathode and their maximum kinetic energy, attained at the top of the cycloid, remains distinctly less than that necessary to produce ionization of the molecules. Under these conditions, the energy of an electron at the moment of a shock diminishes, the result being that the avalanche is no longer sustained, and current then ceases to pass between anode and cathode.

The critical magnetic field depends on the ionization potential, as well as on the dissociation energy of the molecules of gas used, and is substantially proportional to the electrostatic field prevailing between the electrodes. As order of magnitude in the production of an ionization tube according to the inven tion, diameters for the cylindrical electrodes of 3 and 6 centimeters may be mentioned for the internal and external electrode, respectively, between which a potential difference of 40,000 volts is established, corresponding to a maximum electrostatic field on the internal electrode of the order of 4,000,000 volts per meter, acceptable with an argon filling at atmospheric pressure. Under these conditions, the critical magnetic field would be of the order of 2.8 teslas. In operation, the voltage between the electrodes passes from 40,000 volts to 40 volts, representing the voltage drops at the electrodes and the critical magnetic field necessary for extinction is therefore 1,000 times weaker. There is, therefore, nothing to oppose the use of electrostatic fields ten or even 100 times greater, because in the latter case the critical extinction magnetic field would be only 0.28 tesla.

A magnetic field of the order of the tesla is easy to produce in pulses; since 50-cycle industrial frequency is used, a pulse of the order of 50 microseconds duration pennits quenching of the tube at the peak of the sinusoidal whose two zeros are l0,000 microseconds apart, corresponding to two hundred times the width of a pulse.

To fix the ideas, at the center of a turn of ten centimeters in diameter, along which a pulse of 100,000 amperes of peak current is passing, a magnetic field of 1.2 teslas is obtained, that is to say, distinctly greater than the critical magnetic field required in the numerical example mentioned above.

In FIG. 3, an additional coil having turns 24, supplied by its ends 25, produces a weak, permanently applied, constant magnetic field b, superimposed on the blocking magnetic field produced by the bobbin 9 for a very short time. This field b permits rotation of the discharge for distributing the heat dissipation over a larger surface of the electrodes, and its use is necessary whenever the duration of the discharge is sufficient to cause damage to the electrodes. The value b of the field to be produced will be greater, the higher the power is to be dissipated.

Thus, in FIG. 4, a pair of permanent magnets are used for producing the magnetic field b in the axis of the two tubes 27, connected in head-to-tail manner in a 50-cycle single phase AC rectifying circuit.

The circuit is supplied with AC by means of a transformer, whose secondary winding 28, connected at the center tapping to earth 29, is connected by its two ends to the respective anodes of the ionization tubes 27, whose two cathodes are connected together at the terminal 29a of the utilization apparatus 30, connected to earth 31 by its other terminal.

Under these conditions, FIG. 5, the rectified voltage U is represented as a function of time by successive arcs 32. To obtain this result, the tubes 27 are ignited in synchronism with the network by means of a circuit comprising an emitter 33 of coherent magnetic radiation of laser type, supplied from the laser and having its beam 33a oriented parallel to the axis of symmetry of each of the tubes 27, which in turn are arranged symmetrically in space relative to the said beam 33a. A plane mirror 34, whose normal to its surface at its center of symmetry is directed at 45 relative to the incident ray 33a gives a reflected ray 33b of the latter, scanning a plane perpendicular to the said ray 33a, due to the rotation of the mirror 34 about an axis, coincident with the ray 33a. The mirror 34 being rotated in synchronism with the laser, permits ignition of the two tubes at the moment of positive alternation. The reflected ray 33b is shown illuminating the top tube in FIG. 5, while at 330 is shown in dotted line the ray striking the bottom tube after rotation of the mirror through half of revolution, half a period later.

In FIG. 6, the six ionization tubes 35 are distributed in space in a GRETZ rectifying circuit on a chain line circle 36 at the vertices of a regular hexagon, while a coherent electromagnetic radiation synchronized laser transmitter 37 transmits 300 flashes per second and sends a beam 38 to a plane mirror 39, the normal to the reflecting surface of which is inclined at 45 degrees to the beam. The plane mirror 39 rotates in synchronism with the laser about an axis of rotation coinciding with that of the beam 38, imparting to the reflected beam 38a a movement for scanning the plane of the circle 36, such that each tube 35 is ignited by the said beam 380 at the desired moment of the cycle of alternating current passing through it.

In FIG. 7, two tubes 40 are connected head-to-tail in an inverter circuit comprising DC injection at the point 41 connectrng together, across the corresponding blocking coils 42,

the anodes of ionization tubes 40, whose cathodes are connected together across the primary 43a of a transformer 43 having its center tap connected to earth 44, while the secondary winding 43b is connected to the utilization apparatus. The quenching coils are necessary for the deionization of the tubes 40 supplied with direct current, while excitation of the ionization has been efiected at the desired time by a radiation transmitter 32 and rotating mirror 34 system, similar to that used in the rectifying circuit of FIG. 4. However, the choice of the frequency of the inverter being free, it is merely necessary to synchronize the transmitter and the rotation of the mirror to the frequency which it is desired to obtain.

FIG. 8 shows, as a function of the time, the curves of voltage U produced and current delivered by the inverter circuit of FIG. 7.

It is specified that the invention is not limited to the particular form described nor to the applications mentioned, but comprises all the possible modifications corresponding to the general definition which has been given.

Thus, the elimination of the currents induced in the electrodes may involve their subdivision into a larger number of elements by slits parallel to the axis of symmetry of the electrodes and regularly distributed around the said axis.

Likewise, the plane mirrors reflecting the laser beam may be replaced by concave mirrors for converging the said beam better in the interelectrode space.

Likewise, synchronized modulation of the laser beam, both time modulation in transmission and spatial modulation by channelling the beam towards the ionization tubes may be carried out by means of different optical combinations, and more particularly rotating or vibrating the laser.

Likewise, apart from the application of the tubes according to the invention to rectifier or inverter systems, where they function on an all or nothing principle, it is also possible to use their aptitude either to amplify at constant voltage a lowfrequency signal with a considerable gain of power, or to detect a signal by the effect of their quadratic response as a function of the voltage, the magnetic field being kept constant.

It is also possible to use the properties of the ionization tube in the equipment of distribution stations, more particularly for switching heavy currents or for the protection of industrial devices against overvoltages, especially those caused by lightning.

The choice of gas for filling a tube according to the invention is not' critical, and apart from air under pressure, it is possible to use a pure gas, such as nitrogen, argon, helium, sulphur hexafluoride or advantageously a mixture of the latter, ensuring in each application optimum reliability of the ionization tube device.

What is claimed is:

l. A multiple ionization tube arrangement comprising: a plurality of ionization tubes each including two electrodes raised to different potentials and forming between them, an enclosed gastight space containing a gas under pressure; remote control means for said tubes, a laser device emitting a coherent electromagnetic radiation laser beam for controlling ignition of the electric are for each tube, means surrounding said electrodes producing a magnetic field for controlling the extinction of said arc, said electrodes having coaxial surfaces of revolution with the gap separating them at both ends being closed by an insulating synthetic resin, means for rotating said laser beam, said tubes being arranged in an energy exchange circuit wherein the tubes are geometrically positioned such that each tube is sequentially ignited by said beam as it rotates, and means synchronizing the modulation of said laser beam with the scanning movement thereof. 

1. A multiple ionization tube arrangement comprising: a plurality of ionization tubes each including two electrodes raised to different potentials and forming between them, an enclosed gastight space containing a gas under pressure; remote control means for said tubes, a laser device emitting a coherent electromagnetic radiation laser beam for controlling ignition of the electric arc for each tube, means surrounding said electrodes producing a magnetic field for controlling the extinction of said arc, said electrodes having coaxial surfaces of revolution with the gap separating them at both ends being closed by an insulating synthetic resin, means for rotating said laser beam, said tubes being arranged in an energy exchange circuit wherein the tubes are geometrically positioned such that each tube is sequentially ignited by said beam as it rotates, and means synchronizing the modulation of said laser beam with the scanning movement thereof. 